Mr. Weller. This imperfect description is published with hesita- 

 tion, but since the plant evidently belongs in this group, it 

 seems best to refer to it here. The figures speak for themselves, 

 all x 25. The photogravure represents the plant of natural size. 



XITKLLA FLEXILIS (L., ex parte), Ag. 



Chara flexilis, L., ex parte. 



Nitella flexilis, Ag., syst. Alg., 1824. 



Nitella Brogniartiana, Coss, Germ., et. Wedd. Fl., Paris. 



This very common species, while variable as to size and 

 manner of growth, may be recognized easily by being gymno- 

 carpous monoecious, and having abruptly pointed leaves. It 

 varies greatly in size, from a few cm. to as much as 75 cm. and 

 perhaps more in length. In brooks it often forms dense masses 

 or hummocks with rather short stems ; in deeper and slow-flow- 

 ing streams the stems may become excessively elongated. The 

 stems and leaves are variously abbreviated, particularly in fruit- 

 ing specimens, and sometimes, as in Fig. 2 of the plate, the 

 fruiting leaves become densely crowded, vars. nidifica, sub- 

 nidifica, etc. The verticils are composed normally of six leaves, 

 each leaf is once divided into 1-4 terminals, usually two, rarely 

 only one ; the tip of the leaf is abruptly short-pointed, at times 

 almost blunt, never entirely so. Antheridia , about 450 //. in 

 diam.; oogonia, with an evanescent coronula, generally aggrega- 

 ted (i to 3 on one node); oospore about 425 IJL. long, 375 /u. wide, 

 with 6-7 ridges, which are usually sharp, not thick as in N. 

 opaca : membrane of the spore perfectly smooth. 



This species is our most common nitella, found everywhere 

 from the Atlantic to the Pacific, north and south, though at the 

 south it is partly replaced by the larger N. pralonga, A. Br. 

 This species flourishes well in aquaria, and its vigor and clean 

 bright stems make it useful for showing the phenomenon of 

 cyclosis. 



A form with stouter stems and shorter leaves, var. crassa, is 

 now and then met with, but it is usually sterile; a thick autumnal 

 form with but a single terminal, also sterile is sometimes 

 puzzling when sterile. 



In the plate, Fig. i, half the natural size ; Fig. 2, a compact 

 form, natural size, forma subnidifica, well-fruited, from Cali- 

 fornia, Blankinship, Figs. 3-6 x 50; Fig. 7, surface of the smooth 

 spore, showing parts of two sharp ridges highly magnified. 

 Photogravures half the natural size, " n," a more rigid specimen, 



